U.S. patent application number 10/000331 was filed with the patent office on 2002-08-22 for chiral doping agents with variable spiral pitch induction and application thereof to a reflective colour display.
This patent application is currently assigned to ASULAB S.A.. Invention is credited to Chuard, Thierry, Deschenaux, Robert, Klappert, Rolf, Meyer, Severine.
Application Number | 20020114902 10/000331 |
Document ID | / |
Family ID | 8172445 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020114902 |
Kind Code |
A1 |
Chuard, Thierry ; et
al. |
August 22, 2002 |
Chiral doping agents with variable spiral pitch induction and
application thereof to a reflective colour display
Abstract
The present invention concerns chiral doping agents allowing a
modification to be induced in the spiral pitch of a cholesteric
liquid crystal, said doping agents including a biactivated chiral
unit at least one of whose functions allows a chemical link to be
established with an isomerisable group, for example by radiation,
said group possibly having a polymerisable or co-polymerisable end
chain. These new chiral doping agents find application in
particular in a colour display.
Inventors: |
Chuard, Thierry; (Les
Geneveys-sur-Coffrane, CH) ; Deschenaux, Robert; (La
Chaux-de-Fonds, CH) ; Klappert, Rolf; (Neuchatel,
CH) ; Meyer, Severine; (Neuchatel, CH) |
Correspondence
Address: |
SUGHRUE, MION, ZINN,
MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Assignee: |
ASULAB S.A.
|
Family ID: |
8172445 |
Appl. No.: |
10/000331 |
Filed: |
December 4, 2001 |
Current U.S.
Class: |
428/1.1 ;
252/299.2 |
Current CPC
Class: |
C07C 2601/08 20170501;
C09K 19/588 20130101; C09K 19/586 20130101; C07C 2601/14 20170501;
C07D 493/04 20130101; C09K 2323/00 20200801; C07C 245/08 20130101;
C07D 317/32 20130101; Y10T 428/10 20150115 |
Class at
Publication: |
428/1.1 ;
252/299.2 |
International
Class: |
C09K 019/58 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2000 |
EP |
00204584.7 |
Claims
What is claimed is
1. A chiral doping agents allowing modification in the spiral pitch
of a cholesteric liquid crystal composition to be induced, wherein
the chemical structure of said doping agents includes a biactivated
chiral unit, at least one of whose functions allows a chemical link
to be established with an isomerisable group, said group possibly
having a polymerisable or co-polymerisable end chain.
2. The chiral doping agents according to claim 1, wherein they
answer the following formula
1:A.sub.1--Y.sub.1--X--Y.sub.2--A.sub.2 (I)wherein x represents a
chiral radical derived from a biactivated compound, y.sub.1 and
y.sub.2 are identical or different and each represent a functional
linking unit selected from among --O--, --S--, --COO--, --OCO--,
--CON(R)--and --N(R)CO--where R represents an alkyl residue,
A.sub.1 represents a photoisomerisable mesogenic group
corresponding to the formula (II): 21wherein two phenyl residues
.phi. and .phi.' are linked by a photoisomerisable --M--bivalent
radical selected from among --N.dbd.N--, --N.dbd.CH--, --CH.dbd.N--
and --CH.dbd.CH--; said phenyl residues having respectively one or
more substituents R.sub.1, R.sub.2 which are different or identical
selected from among hydrogen, the alkyl or alkoxy radicals from
C.sub.1 to C.sub.5, the halogens, and the cyano, nitro or
trifluoromethyl radicals; and R' represents hydrogen or a group
corresponding to the formula (III):--Y.sub.3--C.sub.nH.sub.2n--Z
(III)wherein Y.sub.3 has the same significance as Y.sub.1 and
Y.sub.2 or represents phenylene, n is an integer number comprised
between 0 and 12 and Z represents hydrogen or a polymerisable
moiety selected from among the acryloyl and acryloyloxy moieties;
and A2 has the same significance as the groups of formula (II) or
formula (III).
3. The chiral doping agents according to claim 2, wherein the
--M--bivalent radical is the radical azo-N.dbd.N-- to form with the
moieties .phi. and .phi.' an azophenyl radical and in that the
substituents R and Y.sub.1 or Y.sub.2 occupy the same ortho, meta
or para positions respectively on moieties .phi. and .phi.'.
4. The chiral doping agents according to claim 2, wherein A.sub.1
and A.sub.2 each correspond to a photoisomerisable mesogenic group
of formula II.
5. The chiral doping agents according to claim 2, wherein A.sub.2
corresponds to the group of formula III.
6. The chiral doping agents according to claim 2, wherein R
represents a group of formula III and in that Z still represents a
polymerisable radical selected from among the acryloyl and
acryloyloxy radicals.
7. The chiral doping agents according to claim 2, wherein the
chiral radical agent X is derived from a diacide or a chiral
diol.
8. The chiral doping agents according to claim 2, wherein the
chiral radical X corresponds to the biactivated radicals derived
from dianhydro-glucitol or dianhydro-mannitol.
9. The chiral doping agents according to claim 8, wherein it
corresponds to the following compound: 2,5-Bis
[4'-(6-acryloyloxyhexyloxy)-2',5'-meth- ylazophenyl-4-carbonyloyl
]-1,4;3,6-dianhydro-D-glucitol.
10. The chiral doping agents according to claim 8, wherein it
corresponds to the following formula:
2-[4'-(6-acryloyloxyhexyloxy)-2',5'-methylazoph- enyl-4
-carbonyloyl]-5-[4-(6-acryloyloxyhexyloxy)
benzoyl]-1,4;3,6-D-gluci- tol.
11. The Method for modulating chiral doping agents according to
claim 1, wherein the modification to the spiral pitch induction of
said chiral doping agents is obtained by ultraviolet (UV), visible
(VIS) or mixed (UV+VIS) radiation acting on the isomerisable group,
the radiation time being controlled to define determined colour
when said doping agents are incorporated in a cholesteric liquid
crystal composition.
12. A display cell including two transparent substrates, supporting
electrodes connected to an electronic circuit, and a sealing frame
delimiting together a lamellar space into which a cholesteric
liquid crystal composition is introduced incorporating at least a
chiral doping agent according to claim 1, wherein the cell is
subjected to ultraviolet (UV) or visible (VIS) radiation modulated
as a function of different zones, or different pixel families by
using masks and varying the radiation time.
13. The display cell according to claim 12, wherein each family of
pixels corresponds to a determined mask allowing the radiation time
of each family to be adjusted.
14. The display cell according to claim 12, wherein masks are
designed to successively uncover each pixel family and to allow the
progressive radiation thereof.
15. The display cell according to claim 12, wherein it does not
include any partitioning, and in that the chiral doping agents
according to claim 1 have a polymerisable or co-polymerisable end
chain.
16. The display cell according to claim 12, wherein it includes
partitions for each zone or for each pixel, and in that the chiral
doping agents according to claim 1 may not include a polymerisable
or co-polymerisable end chain.
Description
[0001] The present invention concerns a new family of chiral doping
agents with variable spiral pitch induction, i.e. chemical
compounds which, when added in small quantities to a nematic type
liquid crystal composition, allow a variable spiral pitch to be
induced as a function of isomerisation of part of the chemical
structure, for example by means of appropriate irradiation whose
wavelength may vary from the ultraviolet (UV) to the visible (VIS),
or by means of a heat gradient.
[0002] The invention concerns more particularly such chiral doping
agents in which the end chains include a polymerisable moiety
allowing the spiral pitch induced by isomerisation to be fixed, and
thus one or more determined colours to be fixed by using a single
liquid crystal composition to which is added a single chiral doping
agent according to the invention or a single composition of said
chiral doping agents.
[0003] In displays operating in reflective mode using chiral
nematic phase materials, also designated by the term "cholesteric",
fixing a colour is known by using:
[0004] a purely optical active substance having a chiral nematic
phase,
[0005] a mixture of optically active substances, all having a
chiral nematic phase, or
[0006] a substance or a mixture of chiral substances having a
nematic phase and containing one or more optically active
substances, i.e. chiral doping agents able to be mesomorphic or not
and capable of inducing helicity having a determined pitch in the
whole mesophase to form a cholesteric phase.
[0007] The compounds according to the present invention correspond
to the chiral doping agents of the last category and belong more
generally to the category of photochemical molecular switches,
certain families of which have already been the subject of numerous
studies and publications which are cited hereinafter by way of
non-exhaustive illustration.
[0008] Photoracemisation of binaphtyl and its derivatives, and
their helicity induction capacity in the nematic medium have been
the subject of in-depth studies in particular by H. J. Deussen
& al (Liq. Cryst. 1996, 21, 327; Mat. Res. Soc. Symp. Proc.
1996, 425, 55). It appears however that the photoisomerisation of
these compounds involves significant decomposition which is
detrimental to the persistence of a determined colour.
[0009] B. L. Feringa & al (J. Am. Chem. Soc. 1991, 113, 5468)
studied thioxanthene type compounds which isomerise reversibly
between two diastereoisomeric forms, with the object of applying
this system to the reversible storage of information and thus also
allowing application to a colour display. These compounds have the
drawback however of having insufficient chemical stability and a
switching speed which is much too long (several minutes, or even
hours), incompatible for example with a digital display in a
timepiece. In the same field, B. L. Feringa's team also studied
derivatives of the dithienylethene type photoisomerisable between
an open shape and a closed form (L. N. Lucas & al Chem. Commun.
1998, 2313; Tetrahedron Lett. 1999, 40, 1775).
[0010] G. B. Schuster & al (J. Am. Chem. Soc. 1995, 117, 8524)
made use of the work of Y. Yokoyama & al (J. Am. Chem. Coc.,
Com. 1995, 785) on fulgide derivatives to modify the helicity of a
cholesteric material. It appears however that a high concentration
(.gtoreq.5%) of fulgide derivatives is required to obtain only a
moderate change in the spiral pitch (approximately 30%).
[0011] H. Hattor & al (Liq. Cryst. 1999, 26, 1085; J. Polym.
Sci. 2000, 38, 887) studied spiropyrane derivatives, and more
particularly compounds obtained via the co-polymerisation of a
cholesterol derivative with different monomers containing a
spiropyrane unit activated on positions other than the nitrogen. It
appears however that the modification of HTP by UV exposure is
insufficient and that modification of the colour reflected by this
material (.DELTA..lambda. approximately 10 nm) is insufficient to
cover the visible spectrum and envisage making a trichromatic
display.
[0012] The works of S. N. Yarmolenko & al (Liq. Cryst. 1994,
16, 877) on photomodulable chiral units derived from menthyl and
the works of R. P. Lemieux & al (Liq. Cryst. 1996, 20, 741; J.
Am. Chem. Soc. 1997, 119, 8111) on photomodulable chiral units
derived from thioindigo may also be cited.
[0013] The chiral molecular photo-switches, whose features were
briefly recalled hereinbefore, practically all integrate the chiral
unit and the photoactive unit in a single entity.
[0014] The chiral doping agents according to the present invention
however include a two-functional chiral unit, at least one of whose
functions allows a chemical bond to be established between an
isomerisable group and thus allows a separate isomerisable group
from the chiral unit to be obtained. In a preferred embodiment, the
isomerisable group has a polymerisable or co-polymerisable end
chain.
[0015] Thus the chiral doping agents according to the invention
have three essential structural characteristics by UV or VIS
radiation and/or by the addition of photoinitiators:
[0016] a biactivated central chiral unit allowing helicity
induction in the nematic phase,
[0017] at least an isomerisable unit allowing the molecular
structure to be varied and thus the helicity to be modulated in the
nematic phase, and
[0018] polymerisable functions allowing, on the one hand the
molecules to be in a way attached by each end and the isomerisation
reaction to be blocked at a determined spiral pitch, thus at a
determined colour, and on the other hand, via the formation of a
gel, preventing the phenomena of diffusion from one pixel to
another when one wishes to realise a trichromatic display, as will
be explained in the detailed description.
[0019] In the following description, "the isomerisable unit " will
be named "photoisomerisable unit " assuming that isomerisation is
obtained by UV or VIS radiation, the chiral doping agents according
to the invention then being named photomodulable chiral doping
agents.
[0020] Other features and advantages of the present invention will
appear more clearly upon reading the following detailed
description, with reference to the annexed drawings, in which:
[0021] FIG. 1 shows a synthesis diagram of a chiral doping agent
according to the invention;
[0022] FIG. 2 shows a synthesis diagram of four chiral doping
agents according to the invention from a common synthesis
intermediate;
[0023] FIGS. 3 and 4 are graphs giving the transmission percentage
as a function of wavelength for two cholesteric liquid crystal
compositions containing a chiral doping agent according to the
invention;
[0024] FIG. 5 shows schematically an embodiment of a trichromatic
cell; and
[0025] FIGS. 6 and 7 are graphs giving the transmission percentage
as a function of wavelength for two embodiments of a trichromatic
cell.
[0026] The photomodulable chiral doping agents according to the
present invention answer more precisely the following formula
I:
A.sub.1--Y.sub.1--X--Y.sub.2--A.sub.2 (1)
[0027] wherein
[0028] X represents a chiral radical derived from a biactivated
compound, such as diacids or diols,
[0029] Y.sub.1 and Y.sub.2 are identical or different and each
represents a functional link unit selected from among --O--, --S--,
--COO--, --OCO--, CON(R)--, --N(R)CO--where R represents an alkyl
moiety,
[0030] A.sub.1 represents a photomerisable group corresponding to
the formula (II) 1
[0031] wherein two phenyl moieties .phi. and .phi.' are linked by a
photomerisable bivalent radical --M-- selected from among
--N.dbd.N--, --N.dbd.CH--, --CH.dbd.N-- and --CH.dbd.CH--; said
phenyl moieties respectively having one or more identical or
different substituents R.sub.1, R.sub.2 selected from among
hydrogen, the alkyl or alkoxy radicals from C.sub.1 to C.sub.5,
halogens and the cyano, nitro or trifluoromethyl radicals; and R'
represents hydrogen or a group corresponding to the formula
(III)
--Y.sub.3--C.sub.nH.sub.2n--Z (111)
[0032] wherein Y.sub.3 has the same significance as Y.sub.1 and
Y.sub.2 or represents phenylene, n may take the values from 0 to 12
and Z represents hydrogen or a polymerisable moiety selected from
among the acryloyl and acryloylxy moieties; and
[0033] A.sub.2 has the same significance as the groups of formula
(II) or formula (III).
[0034] Among the chiral diacids and diols, leading to chiral
radical X of formula (I), one may cite tartric di-O,O'-p-toluyl
tartric acid di-O, O'-p-pivaloyl tartaric acid, 1,2 dicarboxylic
cyclohexane acid, camphric acid, tartric isopropylidene acid,
3-methyladipidic acid, and dianhydro-glucitol and
dianhydro-mannitol, these two diols allowing synthesis of the
preferred compounds as will be seen hereinafter.
[0035] The photoisomerisable unit represented by A.sub.1 and/or
A.sub.2 in formula (I) has azophenyl as its basic structure when M
represents --N.dbd.N--, azomethine when M represents --N.dbd.CH--
and stilbene when M represents --CH.dbd.CH--. As will be seen
hereinafter, the basic structure corresponding to azophenyl has
been retained by way of illustration since it is a simple, easily
synthesised structure whose trans cis equilibrium is well known,
with a displacement towards the cis form by radiation at a
wavelength .lambda. of <400 nm, and a displacement towards the
trans form thermally or by radiation at a wavelength .lambda. of
>400 nm.
[0036] A compound answering the general formula I, and whose
characteristics and properties will be described hereinafter, is
for example the compound referenced 209s answering the formula
hereinafter 2
[0037] wherein the chiral radical X derives from 1,4;
3,6-dianhydro-D-glucitol, Y.sub.1 and Y.sub.2 each representing
--COO--, A.sub.1 and A.sub.2 are identical and each represent an
azophenyl radical (--M--.dbd.--N.dbd.N--), of which a
non-substituted (R.sub.1.dbd.H) phenyl moiety (.phi.) is linked in
para position to --COO--, and the other phenyl moiety (.phi.') of
which disubstituted in 2',5' by a methyl radical
(R.sub.2.dbd.CH.sub.3) further includes in para a chain including
successively --O--(.dbd.Y.sub.3), the hexamethylene radical
(n.dbd.6) and a acryloyloxy polymerisable moiety (.dbd.Z).
[0038] The chemical structures of other compounds illustrating the
family of chiral doping agents according to the invention will be
reported in Table 1 hereinafter with their physico-chemical
characterisation (melting/enthalpy point; elementary analysis).
1TABLE 1 Rf- r- F.degree. C. (.DELTA.H k/mol) ence Structure %
Calc. Trouv. 201b 3 213 (69) C 70,77 70,73 H 4,59 4,67 N 7,50 7,57
201c 4 159 (67) C 71,02 70,82 H 6,17 6,15 N 5,92 5,84 201e 5 134
(40) C 67,56 67,50 H 5,28 5,27 N 5,43 5,41 202c 6 149 (44) C 68,32
68,33 H 7,11 7,10 N 6,37 6,34 203b 7 165 (58) C 72,17 71,99 H 5,30
5,40 N 10,52 10,28 203c 8 195 (64) C 72,11 72,02 H 7,15 7,10 N 7,64
7,71 204c 9 150 (46) C 72,61 72,56 H 7,42 7,40 N 7,36 7,31 206c 10
133 (57) C 68,78 68,77 H 6,71 6,74 N 7,46 7,36 306c 11 63 (41) C
68,78 68,82 H 6,71 6,82 N 7,46 7,20 206e 12 121 (41) C 64,67 64,58
H 5,55 5,69 N 6,71 6,65 207c 13 151 (35) C 71,64 71,57 H 7,27 7,53
N 7,77 7,66 209g 14 204 (62) C 69,27 69,22 H 6,61 6,87 N 7,34 7,47
209j 15 169 (58) C 66,51 66,25 H 6,03 6,13 N 6,20 6,39 209s 16 93
(66) C 67,63 67,61 H 6,52 6,56 N 5,84 5,91 209sf 17 90 (44) C 66,81
66,80 H 6,58 6,51 N 3,39 3,34 209fs 18 89 (46) C 66,81 66,78 H 6,58
6,77 N 3,39 3,49 209sa 19 53 (45) C 65,33 65,27 H 6,31 6,48 N 4,62
4,58 210fs 20 68 (48) C 66,81 66,77 H 6,58 6,78 N 3,39 3,47
[0039] With reference now to the synthesis diagram shown in annexed
FIG. 1, the synthesis of a photoisomerisable and polymerisable
compound having the reference 201e in Table 1 will be described
hereinafter.
EXAMPLE 1
Synthesis of 2,3-Bis[di-4, 4' (4-acryloyloxybutyloxy)
azonhenyl-carbonyloy]-di-O, O'-p-toluyl-L-tartrate (Ref 201 e)
[0040] Synthesis of this compound is effected in three steps.
[0041] 1st step: Preparation of the 4.4'-hydroxy-azobenzene
intermediate (200a)
[0042] 10.0 g (71.9 mmol) of 4-nitrophenol are finely pounded in a
mortar with 50.0 g (891.0 mmol) of KOH. The mixture is placed in a
porcelain cupel, 10 ml of water are added and the mixture is gently
heated and stirred until a homogenous paste is obtained. The heat
is then increased and the mixture progressively passes from yellow
to violet-black in a vigorous reaction with gas emission. When the
gas emission has finished, heating is then stopped. The solid is
dissolved while still hot in a minimum of water (approx. 150 ml)
and the pH of the solution thereby obtained is brought to between 8
and 9 while being stirred with HCl 5N. A colour change from dark
brown to beige occurs in addition to the formation of a precipitate
which is filtered on a Buchner funnel and vacuum oven dried in the
presence of P.sub.2O.sub.5 to give 5.8 g of raw product. The latter
is purified by silicon gel chromatography with ether as eluant. The
fraction containing the pure product is evaporated to dryness,
giving 4.62 g of product corresponding to the reference 200a (60%
yield).
[0043] 2nd step: Preparation of the
4-hydroxy-4'(4-acryloyloxybutyloxy)-az- obenzene intermediate
(200e)
[0044] 0.8 g (3.73 mmol) of compound 200a and 0.54 g (3.73 mmol) of
4-hydroxybutylacrylate are dissolved in 20 ml of dry THF. 1.00 g
(3.8 mmol) of triphenylphosphine are added and the solution is
cooled to 0 .degree. C. 1.7 ml (3.74 mmol) of a solution of 40%
DEAD (diethylazodicarboxylate) in toluene are added drop by drop
then left to react overnight at ambient temperature. The solvent is
removed in a rotating evaporator to give 3.2 g of raw product which
is purified by silicon gel chromatography with a
CH.sub.2Cl.sub.2/AcOEt (97:3) eluant. After removing the solvent,
one of the fractions collected allows 0.48 g of product to be
obtained corresponding to the reference 200e (36% yield).
[0045] 3rd step: Obtaining the title compound
[0046] 0.49 g (1.28 mmol) of (-)-di-O,O'-p-toluyl-L-tartric acid,
0.55 g (2.67 mmol) of DCC (N,N'-dicyclohexylcarbodiimide) and 0.8 g
(2.68 mmol) of compound 200e are dissolved in 70 ml of dry
CH.sub.2Cl.sub.2 and cooled to 0.degree. C. 0.04 g (0.33 mmol) of
4-DMAP (4-dimethylamino pyridine) are added and the reactional
mixture is stirred for seven hours at 0.degree. C. before being
washed with HCl 0.01 N. The organic phase is dried on MgSO4 and the
solvent removed in a rotating evaporator, to give 1.62 g of raw
product. The latter is purified by silicon gel chromatography with,
at the beginning, an eluant of CH.sub.2Cl.sub.2/AcOEt (98:2), then
CH.sub.2Cl.sub.2/AcOEt (94:6). 0.76 g of product are isolated and
hot recrystallised in EtOH, to give 0.40 g of the title product
(33% yield).
[0047] In addition to the characteristics listed in Table 1, the
nuclear magnetic resonance spectrum and mass spectrum were also
effected which confirm the structure and purity of the expected
product: .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.82-1.98 (m, 8H,
aliph.); 2.45 (s, 6H, CH.sub.3); 4.09 (t, 4H, OCH.sub.2); 4.26 (t,
4H, CO.sub.2CH.sub.2); 5.82 (dd, 2H, vinyl.); 6.13 (dd, 2H,
vinyl.); 6.40 (s, 2H, CH); 6.42 (dd, 2H, vinyl.); 6.99 (d, 4H,
arom.); 7.19 (d, 4H, arom.); 7.31 (d, 4H, arom.); 7.85 (d, 4H,
arom.); 7.88 (d, 4H, arom.); 8.10 (d, 4H, arom.). MS: 1031
(M+H).sup.+.
[0048] With reference now to the synthesis diagram shown in annexed
FIG. 2, the synthesis of the compounds having the references 209s,
209sf, 209 fs and 209sa in Table 1 will be described in examples 2
to 5 hereinafter.
EXAMPLE 2
Synthesis of 2.5
Bis[4'-(6-acryloyloxyhexyloxy)-2.5'-methylazophenyl-4
-carbonyloyl]-1.4;3.6-dianhydro-D.glucitol (209s)
[0049] This synthesis is effected in five steps since it is
necessary to prepare a reactive form of substituted azobenzene,
which is not a commercial product.
[0050] 1 st step: Preparation of the 2.5-dimethyl-4-hydroxy-4
'-methoxycarbonyl-azobenzene intermediate (200p)
[0051] 5.00 g (33.1 mmol) of methyl 4-aminobenzoate are dissolved
in 40 ml HCl 3N and cooled to 0.degree. C. A solution of 2.76 g
(40.0 mmol) of NaNO.sub.2 in 15 ml of water is added drop by drop
then the mixture is stirred for an other hour at 0.degree. C. 0.57
g (9.54 mmol) of urea are added to destroy the excess NaNO.sub.2.
The reactional mixture is then poured into a solution at 0.degree.
C. of 4.04 g (33.1 mmol) of 3,5-dimethylphenol in 40 ml of NaOH 2N
causing the formation of a very dense orange precipitate. The
precipitate is filtered on a Buchner funnel and vacuum oven dried
in the presence of P.sub.2O.sub.5, leading, after hot
recrystallisation in toluene to 7.83 g of product having the
reference 200p (83% yield).
[0052] 2nd step: Preparation of the
2.5-dimethyl-4-(6-hydroxyhexyloxy) azobenzene intermediate
(200g)
[0053] 8.00 g (28.1 mmol) of 200p are dissolved in 160 ml of dry
EtOH and 1.13 g (28.2 mmol) of NaOH are added. The mixture is
refluxed with heating and 3.80 g (27.8 mmol) of 6-chloro-1-hexanol
are added. The reflux is maintained for six days adding two further
portions of 3.80 g (27.8 mmol) of 6-chloro-1-hexanol (after one and
four days of reaction respectively). After cooling, the mixture is
concentrated to approximately 100 ml in a rotating evaporator
apparatus and decanted into a separating funnel. 300 ml of ether
are added and the organic phase is washed with HCl 1N. As the
aqueous phase is orange-coloured, the latter is extracted once with
ether. The organic phases are grouped, dried over MgSO.sub.4 and
the solvent is removed in a rotating evaporator apparatus, giving a
viscous residue which is purified by silicon chromatography with a
CH.sub.2Cl.sub.2/AcOEt (95:5) eluant. This operation allows a
fraction containing the product referenced 200q to be obtained,
which is evaporated to dryness to give 11.7 g of product in oily
form.
[0054] 3rd step: Preparation of the
2'.5'-dimethyl-4'-(6-hydroxyhexyloxy)-- 4 -azophenylcarboxylic acid
intermediate (200r)
[0055] The oil obtained in the preceding step (11.7 g) is dissolved
in 150 ml of EtOH and 200 ml of water containing 9.00 g (225 mmol)
of NaOH are added and the mixture is refluxed with heating for
three hours. After cooling, the mixture is poured into a water/ice
bath and the solution is acidified with HCl 5N. The orange
precipitate is filtered on a Buchner funnel and vacuum oven dried
in the presence of P.sub.2O.sub.5. Hot recrystallisation in AcOEt
gives 3.46 g of product having the reference 200r (33% yield
calculated from the initial quantity of 200p).
[0056] 4th step: Preparation of the
2'.5'-dimethyl-4'-(6-acryloyloxyhexylo- xy)-4 -azophenylcarboxylic
acid intermediate (200s)
[0057] 3.00 g (8.10 mmol) of 200r and 2.40 g (19.8 mmol) of
N,N-dimethylaniline are dissolved, by heating if necessary in 200
ml of THF (tetrahydrofurane). 0.90 g (9.94 mmol) of acryloyle
chloride are added at ambient temperature. The mixture is stirred
for two days at ambient temperature adding a further 2.40 g (19.8
mmol) of N,N-dimethylaniline and 0.90 g (9.94 mmol) of acryloyle
chloride after one day. The reactional mixture is decanted into a
separating funnel, 200 ml of ether are added and the organic phase
is washed with HCl 2N. The organic phase is dried and the solvent
removed in a rotating evaporator. The residue is purified by
silicon gel chromatography with ether as eluant. The fraction
containing the pure product is evaporated to dryness, leading to
3.16 g of product having the reference 200s (92% yield) which can
be recrystallised in an ether/hexane mixture.
[0058] Step 5: Obtaining the title product 2.23 g (5.33 mmol) of
200s are dissolved in 200 ml of DME (1.2-dimethoxyethane) and
cooled to -25.degree. C. 0.60 g. (5.24 mmol) of CH.sub.3SO.sub.2Cl
then 1.10 g (10.87 mmol) of TEA (triethylamine) are added and the
mixture is kept one hour at -25.degree. C. 0.36 g (2.46 mmol) of
dianhydro-D-glucitol and 0.65 g (5.32 mmol) of 4-DMAP are added.
Cooling is stopped and the reactional mixture is stirred for
another three days at ambient temperature before being hydrolysed
with diluted aqueous HCl and decanted into a separating funnel. 200
ml of CH.sub.2Cl.sub.2 are added then the organic phase is
separated, dried on MgSO.sub.4 and the solvent removed in a
rotating evaporator. The residue is purified by two successive
silicon gel chromatography operations with respectively
CH.sub.2Cl.sub.2/AcOEt (94:6) and CH.sub.2Cl.sub.2/AcOEt (96:4)
mixtures as eluants. The fraction containing the pure product after
the second column is evaporated to dryness leading to 0.78 g of a
solid which is recrystallised twice in hot air in EtOH, leading to
0.24 g of the title product (10% yield).
[0059] In addition to the characteristics listed in Table 1, the
nuclear magnetic resonance spectrum and the mass spectrum were also
effected which confirm the structure and purity of the expected
compound: .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.41-1.61 (m, 8H,
aliph.); 1.65-1.93 (m, 8H, aliph.); 2.54 (s, 12H, CH.sub.3); 4.03
(t, 4H, OCH.sub.2); 4.10-4.22 (m, 4H, CO.sub.2CH.sub.2; 4H,
CO.sub.2CHCH.sub.2); 4.74 (d, 1H, CO.sub.2CHCH); 5.12 (t, 1H,
CO.sub.2CHCH); 5.48 (ddd, 1H, CO.sub.2CH); 5.54 (m, 1H,
CO.sub.2CH); 5.83 (dd, 2H, vinyl.); 6.13 (dd, 2H, vinyl.); 6.42
(dd, 2H, vinyl.); 6.68 (s, 4H, arom.); 7.86 (d, 4H, arom.); 8.16
(d, 2H, arom.); 8.23 (d, 2H, arom.). MS : 959 (M).sup.+.
EXAMPLE 3
[0060]
2-[4'-(6-acryloyloxyhexyloxy)-2'.5'-methylazophenyl-4-carbonyloy]---
5-[4-(6-acryloyloxyhexyloxy)benzoyl]-1.4:3.6-D-qlucitol (209sf)
[0061] As can be seen in the formula developed in Table 1, this
compound has only one photo-isomerisable group. In order to obtain
it the operating conditions of the fifth step of example 3 are
modified, in particular by using a high excess of
dianhydro-D-glucitol and a shorter reaction time, so as to obtain
first of all a mono-ester. The different reactivity of the endo and
exo forms, and their different behaviour during silicon gel
chromatography allow one to obtain selectively the exo form which
will be used in the present example or the endo form which will be
used, in the two following examples.
[0062] 1st step: Obtaining 209s-mono-ester-exo and
209s-mono-ester-endo intermediates
[0063] 4.15 g (9.78 mmol) of 200s are dissolved in 200 ml of DME
and cooled to -30.degree. C. 1.12 g (10.56 mmol) of
CH.sub.3SO.sub.2Cl then 2.12 g (20.95 mmol) of TEA are added and
the mixture is maintained for 1 h30 at -300.degree. C. A solution
of 9.5 g (65.00 mmol) of dianhydro-D-glucitol in 50 ml of DME then
1.30 g (10.64 mmol) of 4-DMAP are added. Cooling is stopped and the
reactional mixture is stirred overnight at ambient temperature
before being hydrolysed with diluted aqueous HCl and decanted into
a separating funnel. The aqueous phase is extracted with
CH.sub.3Cl.sub.3 until it becomes colourless. The organic phases
are regrouped, dried over MgSO.sub.4 and the solvent removed in a
rotating evaporator leading to 6.0 g of a solid which is purified
by silicon gel chromatography.
[0064] A first fraction with CH.sub.2Cl.sub.2/AcOEt (95:5) as
eluant is collected containing inter alia the diesterification
product 209s. A second fraction with CH.sub.2Cl.sub.2/AcOEt (85:15)
as eluant is collected, evaporated to dryness and the solid thereby
obtained is hot recrystallised in hexane, leading to 1.30 g of
209s-mono-ester-exo (24% yield).
[0065] The nuclear magnetic resonance spectrum of this compound is
as follows:
[0066] .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.41-1.62 (m, 4H,
aliph.); 1.68-1.93 (m, 4H, aliph.); 2.53 (s, 6H, CH.sub.3); 3.64
(dd, 1H, CH(OH)CH.sub.2); 3.96 (dd, 1H, CH(OH)CH.sub.2); 4.02 (t,
2H, OCH.sub.2CH.sub.2); 4.10-4.22 (m, 2H, CO.sub.2CH.sub.2; 2H,
CO.sub.2CHCH.sub.2); 4.37 (ddd, 1H. CHOH); 4.67 (d, 1H,
CO.sub.2CHCH); 4.75 (t, 1H, CH(OH)CH); 5.51 (d, 1H, CO.sub.2CH);
5.82 (dd, 1H, vinyl.); 6.12 (dd, 1H, vinyl.); 6.41 (dd, 1H,
vinyl.); 6.67 (s, 2H, arom.); 7.86 (d, 2H, arom.); 8.15 (d, 2H,
arom.).
[0067] A third fraction with CH.sub.2Cl.sub.2/AcOEt (75:25) as
eluant is collected, evaporated to dryness and the solid thereby
obtained is hot recrystallised in hexane to lead to 2.59 g of
209s-mono-ester-endo (48% yield).
[0068] The nuclear magnetic resonance spectrum of this compound is
as follows:
[0069] .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.42-1.61 (m, 4H,
aliph.); 1.66-1.86 (m, 4H, aliph.); 2.54 (s, 6H, CH.sub.3);
3.93-4.05 (m, 2H, OCH.sub.2CH.sub.2; 2H, CO.sub.2CHCH.sub.2; 2H,
CH(OH)CH.sub.2); 4.19 (t, 2H, CO.sub.2CH.sub.2); 4.39 (m, 1H,
CHOH); 4.47 (d, 1H, CH(OH)CH); 5.02 (t, 1H, CO.sub.2CHCH); 5.43
(ddd, 1H, CO.sub.2CH); 5.82 (dd, 1H, vinyl.); 6.13 (dd, 1H,
vinyl.); 6.41 (dd, 1H, vinyl.); 6.67 (s, 2H, arom.); 7.87 (d, 2H,
arom.); 8.19 (d, 2H, arom.).
[0070] 2nd step: Obtaining the title compound
[0071] 3.67 g (12.55 mmol) of 4-(6-acryloyloxhexyloxy)benzoic acid
are dissolved in 150 ml of DME and cooled to -25.degree. C. 1.42 g
(12.40 mmol) of CH.sub.3SO.sub.2Cl then 2.54 g (25.10 mmol) of TEA
are added and the mixture is maintained one hour at -25.degree. C.
3.34 g (6.04 mmol) of 209s-mono-ester-exo prepared in the preceding
step dissolved in 30 ml of DME then 0.76 g (6.22 mmol) of 4-DMAP
are added. Cooling is stopped and the reactional mixture is stirred
one more night at ambient temperature before being refluxed with
heatingfor six hours. After cooling, the reactional mixture is
hydrolysed with diluted aqueous HCl and decanted into a separating
funnel. The aqueous phase is extracted with CH.sub.2Cl.sub.2 until
the aqueous phase is colourless. The organic phases are grouped,
dried on MgSO.sub.4 and the solvent removed in a rotating
evaporator, giving residue which is purified by silicon
chromatography with a CH.sub.2Cl.sub.2/AcOEt (96:4) eluant. The
fraction containing the pure product is evaporated to dryness and
the solid hot recrystallised in EtOH, leading to 3.65 g of the
title product (73% yield).
[0072] In addition to the characteristics noted in Table 1, the
nuclear magnetic resonance spectrum and the mass spectrum were
effected, which confirm the purity and structure of the expected
product:
[0073] .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.42-1.60 (m, 8H,
aliph.); 1.67-1.95 (m, 8H, aliph.); 2.54 (s, 6H, CH.sub.3);
4.00-4.22 (m, 4H, CO.sub.2CH.sub.2; 4H, OCH.sub.2CH.sub.2; 4H,
CO.sub.2CHCH.sub.2); 4.72 (d, 1H, CO.sub.2CHCH); 5.09 (t, 1H,
CO.sub.2CHCH); 5.43 (ddd, 1H, CO.sub.2CH); 5.52 (m, 1H,
CO.sub.2CH); 5.83 (dd, 2H, vinyl.); 6.13 (m, 2H, vinyl.); 6.42 (m,
2H, vinyl.); 6.68 (s, 2H, arom.); 6.93 (d, 2H, arom.); 7.86 (d, 2H,
arom.); 8.04 (d, 2H, arom.); 8.15 (d, 2H, arom.). MS: 827
(M+H).sup.+.
EXAMPLE 4
2-[4-(6-acryloyloxyhexyloxy)benzoyl]-5-[4'-(6
-acryloyloxyhexyloxy)-2',5'--
methylazophenyl-4-carbonyloyl]-1,4;3,6-D-glucitol (209fs)
[0074] 4.40 g (15.05 mmol) of 4-(6-acryloyloxyhexyloxy) benzoic
acid are dissolved in 200 ml of DME and cooled to -25.degree. C.
1.70 g (14.84 mmol) of CH.sub.3SO.sub.2Cl then 3.04 g (30.04 MMOL)
of TEA are added and the mixture is maintained one hour at
-25.degree. C. 4.01 g (7.26 mmol) of 209s-monoester-endo dissolved
in 30 ml of DME then 0.88 g (7.20 mmol) of 4-DMAP are added.
Cooling is stopped and the reactional mixture is stirred for one
more night at ambient temperature before being refluxed with
heating for six hours. After cooling, the mixture is hydrolysed
with diluted aqueous HCl and decanted into a separating funnel. The
aqueous phase is extracted with CH.sub.2Cl.sub.2 until the aqueous
phase is colourless. The organic phases are grouped, dried on
MgSO.sub.4 and the solvent removed in a rotating evaporator,
leading to a residue which is purified by silicon chromatography
with a CH.sub.2Cl.sub.2/AcOEt (96:4) eluant. The fraction
containing the pure product is evaporated to dryness and the solid
hot recrystallised in EtOH, giving 4.21 g of the title product (70%
yield).
[0075] In addition to the characteristics noted in Table 1, the
nuclear magnetic resonance spectrum was effected, which confirms
the purity and structure of the expected product:
[0076] .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.42-1.62 (m, 8H,
aliph.); 1.67-1.95 (m, 8H, aliph.); 2.54 (s, 6H, CH.sub.3);
3.98-4.22 (m, 4H, C.sub.2CH.sub.2; 4H, OCH.sub.2CH.sub.2; 4H,
CO.sub.2CHCH.sub.2); 4.69 (d, 1H, CO.sub.2CHCH); 5.08 (t, 1H,
CO.sub.2CHCH); 5.42-5.50 (m, 2H, CO.sub.2CH); 5.82 (dd, 2H,
vinyl.); 6.12 (m, 2H, vinyl.); 6.41 (m, 2H, vinyl.); 6.68 (s, 2H,
arom.); 6.90 (d, 2H, arom.); 7.88 (d, 2H, arom.); 7.96 (d, 2H,
arom.); 8.21 (d, 2H, arom.).
EXAMPLE 5
[0077] 2-[4'-(6-acryloyloyloxyhexyloxy)-2'.5'-methylazophenyl-4
-carbonloyl]-5-acrylyloyl-1.4;3.6-D-glucitol (209sa)
[0078] Like the compounds of examples 3 or 4, this compound
includes only one photoisomerisable group, but it differs therefrom
in that the non-photoisomerisable (but polymerisable) chain is
shorter. It is obtained via the action of acrylic acid on
mono-ester-endo (209s-mono-ester-endo) of dianhydro-D-glucitol, as
explained hereinafter.
[0079] 1.95 g (3.53 mmol) of 209s-mono-ester-endo are dissolved in
40 ml of THF. 2.40 g (19.8 mmol) of N,N-dimethylaniline then 1.00 g
(11.0 mmol) of acryloyle chloride are added at ambient temperature.
The mixture is stirred at ambient temperature for 5 days. The
reactional mixture is concentrated to 5-10 ml taking care not to
overheat it, then chromatography is rapidly effected with
CH.sub.2Cl.sub.2/AcOEt (95:5) as eluant with the aim of removing
the excess acryloyle chloride and thus reducing the risk of
polymerisation. A fraction is collected and washed with NaOH 1N
then HCl 1N. After drying on MgSO.sub.4, the solvent is removed in
a rotating evaporator leading to, a residue which is immediately
purified by silicon chromatography. A first fraction with
CH.sub.2Cl.sub.2 as eluant is collected containing impurities. The
fraction with the desired product is eluted with
CH.sub.2Cl.sub.2/AcOEt (95:5) as eluant. After removing the
solvent, an oil is obtained which is crystallised after hot
dissolution in EtOH. giving 1.0 g of the title product (47%
yield).
[0080] In addition to the characteristics noted in Table 1, the
nuclear magnetic resonance spectrum was effected, which confirms
the purity and structure of the expected product:
[0081] .sup.1H-RMN (200 MHz, CDC.sub.3): 1.42-1.92 (m, 8H, aliph.);
2.55 (s, 6H, CH.sub.3); 4.00-4.22 (m, 2H, CO.sub.2CH.sub.2; 2H,
OCH.sub.2CH.sub.2; 4H, CO.sub.2CHCH.sub.2); 4.61 (d, 1H,
CO.sub.2CHCH); 5.04 (t, 1H, C.sub.2CHCH); 5.34 (m, 1H, CO.sub.2CH);
5.45 (ddd, 1H, CO.sub.2CH); 5.83 (dd, 2H, vinyl.); 6.13 (m, 2H,
vinyl.); 6.42 (m, 2H, vinyl.) 6.68 (s, 2H, arom.); 7.88 (d, 2H,
arom.); 8.20 (d, 2H, arom.).
EXAMPLE 6
[0082] 2-[4'-(6-acryloyloxyhexyloxy)-2',5'-methylazophenyl-4
-carbonyloy]-5-[4-(6-acryloyloxyhexyloxy)
benzoyl]-1,4;3,6-D-mannitol (210 fs)
[0083] This compound, which is a diastereoisomer of the compound
described in example 3, is prepared from
1,4;3.6-dianhydro-D-mannitol with a few modifications to the
experimental process. The synthesis diagram is not reproduced in
FIG. 1.
[0084] 1st step: Preparation of the monosubstituted 1.4;3.
6-dianhydro-D-mannitol intermediate (110f-mono-ester)
[0085] 2.00 g (6.84 mmol) 4-(6-acryloyloxyhexyloxy) benzoic acid
are dissolved in 150 ml of DME and cooled to -25.degree. C. 0.80 g
(6.84 mmol) of CH.sub.3SO.sub.2Cl then 1.40 g (13.83 mmol) of TEA
are added and the mixture is maintained one hour at -25.degree. C.
A solution of 3.00 g (20.53 mmol) of 1,4;3, 6-dianhydro-D-mannitol
in 50 ml of DME then 2.50 g (20.46 mmol) of 4-DMAP. Cooling is
stopped and the reactional mixture is stirred for one more day at
ambient temperature before being hydrolysed with diluted aqueous
HCl and decanted into a separating funnel. 300 ml of
CH.sub.2Cl.sub.2 are added and the organic phase is separated,
dried on MgSO.sub.4 then the solvent is removed in a rotating
evaporator, causing polymerisation of a part of the product. The
remaining part is rapidly dissolved in CH.sub.2Cl.sub.2 then
purified by silicon chromatography with a CH.sub.2Cl.sub.2/AcOEt
(75:25) eluant. The fraction containing the pure product is
evaporated to dryness and the solid hot recrystallised in EtOH,
again causing polymerisation of part of the product. The polymer is
removed by filtering and the solution is left to crystallise at
ambient temperature then in the refrigerator, finally leading to
0.84 g of the product having the reference 110f-mono-ester (29%
yield).
[0086] 2nd step: Obtaining the title compound
[0087] 420 mg (0.99 mmol) of the compound prepared in the fourth
step of example 1 (200s) are dissolved in 100 ml of DME and cooled
to -25.degree. C. 113 mg (0.99 mmol) of CH.sub.3SO.sub.2Cl then 200
mg (1.98 mmol) of TEA are added and the mixture is maintained one
hour at -25.degree. C. 800 mg (1.90 mmol) of the 11 Of-mono-ester
intermediate prepared in the first step and 121 mg (0.99 mmol) of
4-DMAP are added. Cooling is stopped and the reactional mixture is
agitated for one more day at ambient temperature before being
hydrolysed with diluted aqueous HCl and decanted into a separating
funnel. 400 ml of ether are added then the organic phase is
separated, dried on MgSO.sub.4 and the solvent is removed in a
rotating evaporator. The residue obtained is purified a first time
by silicon gel chromatography with a CH.sub.2Cl.sub.2/AcOEt (90:10)
eluant, then a second time with a CH.sub.2Cl.sub.2/AcOEt (95:5)
eluant. The fraction containing the pure product is evaporated to
dryness leading to 109 mg of the title product (13% yield).
[0088] In addition to the characteristics noted in Table 1, the
nuclear magnetic resonance spectrum and mass spectrum were
effected, which confirm the purity and structure of the expected
product:
[0089] .sup.1H-RMN (200 MHz, CDCl.sub.3): 1.41-1.61 (m, 8H,
aliph.); 1.65-1.93 (m, 8H, aliph.); 2.54 (s, 6H, CH.sub.3); 4.02
(t, 4H, OCH.sub.2CH.sub.2); 4.10-4.27 (m, 4H, CO.sub.2CH.sub.2; 4H,
CO.sub.2CHCH.sub.2); 4.87-4.95 (m, 2H, CO.sub.2CHCH); 5.29-5.43 (m,
2H, CO.sub.2CH); 5.83 (dd, 2H, vinyl.); 6.13 (dd, 2H, vinyl.); 6.42
(dd, 2H, vinyl.); 6.68 (s, 2H, arom.); 6.92 (d, 2H, arom.); 7.88
(d, 2H, arom.); 8.05 (d, 2H, arom.); 8.23 (d, 2H, arom.). MS :827
(M+H).sup.+.
[0090] The experiments conducted, reported in examples 7 and 8
hereinafter, show that the chiral doping agents according to the
invention allow the optical properties of a medium to be modified,
and in particular, they allow a variable spiral pitch to be induced
in a nematic liquid crystal medium as a function of the nature and
duration of radiation whose wavelength may vary from visible (VIS)
to ultraviolet (UV). In a preferred application, the properties of
the chiral doping agents according to the invention are implemented
to make a trichromatic display.
EXAMPLE 7
Specific Rotation, Solubility and HTP
[0091] For the above indicated application, the compounds must have
high solubility and HTP in a nematic. These values, for a certain
number of compounds according to the invention are recorded in
Table 2 hereinafter. In this Table, the value of the specific
rotation [a].sub..lambda..sup.20 before and after isomerisation,
has been recorded for the methylene chloride concentrations
indicated, and for the wavelengths mentioned.
2TABLE 2 Concen- tration Com- g/100 ml [.alpha.].sup.20.lambda.
Solubility s HTP pound CH.sub.2Cl.sub.2) before iso. after iso. (%
mass) (.mu.m.sup.-1) 201c 0.06 -64.degree..sub.546
-135.degree..sub.546 1.5% < s < 3.0% 20 201e 0.1
-60.degree..sub.546 -114.degree..sub.546 1.5% < s < 3.0% 19
206c 0.09 -222.degree..sub.546 -81.degree..sub.546 0.6% < s <
0.8% 13 206e 0.09 -177.degree..sub.546 -19.degree..sub.546 3.0%
< s < 4.0% 11 209s 0.05 -248.degree..sub.578
-129.degree..sub.578 3.0% < s < 3.9% 35 209sf 0.06
-85.degree..sub.578 -47.degree..sub.578 4.0% < s 35 210fs 0.06
+221.degree..sub.578 +198.degree..sub.578 1.9% < s < 6.0%
17
[0092] With the exception of compound 210fs, it will be observed
that the other compounds show a remarkable modification in their
optical rotation, mostly greater than 50% which shows their
aptitude to isomerisation by radiation. This Table further confirms
what was already known, namely the absence of any evident
correlation between the specific rotation variation and the HTP
value of the compounds. This Table shows that, for the majority of
the compounds studied, solubility is of the order of 3% in weight
or greater and that HTP varies between 11 .mu.m.sup.-1 and 35
.mu.m.sup.-1.
EXAMPLE 8
Photomodulation of the Colour of Display Cells
[0093] By way of example, for the experiences recorded hereinafter,
chiral compound 209s was used, which has a quite high HTP of 35
.mu.m.sup.-1 and good solubility allowing it to be incorporated in
a concentration of 3.3% in a basic cholesteric material, including
in particular a nematic mixture formed of biphenyls (for example
available from Merck under the reference E48). The compound thus
prepared is introduced into a test cell including a front substrate
and a back substrate, these substrates being formed by glass
plates, of 2.2.times.2.8 mm and 0.3 mm thick held by a sealing
frame at a spacing of 6 .mu.m. The cell includes an non brushed
planar alignment layer, and a 1 cm square shape pixel including on
each of the substrates an indium tin oxide (ITO) coating forming
the electrodes which will allow the cell to switch from one state
to another by applying an electric field. Once filled, the cell is
exposed to UV radiation and the evolution of the UV-VIS spectrum is
followed as a function of exposure time.
[0094] In the experiment corresponding to the graph of FIG. 3,
giving the transmission percentage as a function of wavelength,
only chiral doping agent 209s has been added to the basic
cholesteric material and the initial state (curve a) and the
spectrum respectively after 1 minute (curve b), 3 minutes (curve c)
and 10 minutes exposure (curve d) are shown. A longer exposure time
no longer modifies the spectrum, curve d representing the cell
spectrum photomodulated to the maximum. A displacement will then be
observed reaching 160 nm from the initial spectrum, i.e. a
displacement from violet blue (curve b) to orange-red (curve d),
passing through green (curve c).
[0095] In the experiment corresponding to the graph of FIG. 4, 3%
in weight of a photoinitiator of the morpholinocetone type,
commercially available from Ciba-Geigy under the reference
Irgacure.RTM.369, has been added to the basic cholesteric material.
This photoinitiator aims to improve polymerisation of the end
chains. For the purpose of improving polymerisation and thus the
fixing of a determined colour, the photoinitiator may also be
replaced by a discrylate type comonomer, such as the compound RM-82
available from Merck. It is also possible to use simultaneously, in
appropriate ratios, both a photoinitiator and a comonomer. With
reference now to FIG. 4, which concerns a cell whose basic
cholesteric material only contains one doping agent according to
the invention and a photoinitiator. Four curves representing
respectively the initial state (curve a), the spectrum after 2
minutes (curve b), 5 minutes (curve c) and 18 minutes (curve d) are
shown. A variation of 190 nm can be observed between the initial
spectrum and the spectrum of the cell photomodulated to the
maximum.
[0096] By replacing chiral doping agent 209s with chiral doping
agent 209sf at a concentration of 4.1% in weight, in the above
experiment, a variation of 220 nm would be observed after 5 minutes
in the same conditions.
EXAMPLE 9
First Embodiment of a Trichromatic Cell
[0097] Compound 209sf (example 4) which showed a very good aptitude
for modifying the spiral pitch of the cholesteric material with a
window of 220 nm was used for the preparation of multi-coloured
display cells. From identical cells to those used in example 8 with
no partitions and containing only one monochrome material a cell
with three zones of different colour (blue, green and red) was made
by selectively or progressively masking three zones allowing their
respective radiation rate to be modulated.
[0098] Such trichromatic cells may either display information, or
be used as a coloured filter in a display assembly.
[0099] In a so-called "dissociative " process, each family of
pixels is individually photomodulated, the two other families of
pixels being covered by a mask forming a barrier to the rays, the
process being repeated for each of the three families varying the
radiation time of each family.
[0100] Of course, since a display cell includes a very large number
of pixels of very small dimensions, the masking operations are
effected by means of masks formed or obtained by known methods such
as photolithographic techniques.
[0101] This process is schematically shown in FIG. 5. It can be
seen that, starting from a chemical composition of an identical
cholesteric material CM for all the pixels, in a first step 1 a
family of blue pixels (B), then in a second step 2 a family of
green pixels (G), and in a third step 3 a family of red pixels (R)
are created to form a trichromatic display CD.
[0102] The graph of FIG. 6 gives the transmission percentage as a
function of wavelength, at the initial state (curve a), for the
blue-coloured pixels (curve B), for the green-coloured pixels
(curve G) and for the red-coloured pixels (curve R).
EXAMPLE 10
Second Embodiment of a Trichromatic Cell
[0103] In this second embodiment pixelisation is achieved in
accordance with a so-called "additive " process. The entire cell,
i.e. all the pixels having to define the three colours, is
subjected to a first period of exposure, then a family of pixels is
masked and the exposure is continued for a second period and
finally a second family of pixels different from the preceding one
is in turn masked and exposure is finished during a third
period.
[0104] With a cell having the same features as those of example 9,
and for identical exposure periods for each pixel family, the graph
giving the transmission percentage as a function of wavelength
shown in FIG. 7 is obtained.
[0105] Comparing the graphs of FIGS. 6 and 7, it will be observed
that there are no significant differences between the "dissociative
" process and the "additive" process.
EXAMPLE 11
Third Embodiment of a Trichromatic Cell
[0106] In the embodiments of examples 9 and 10 hereinbefore, it was
indicated that there was no partitioning between the bottom
substrate and the top substrate to delimit the individual pixels.
These embodiments are satisfactory when strong polymerisation of
the medium can be obtained. In the opposite case, and according to
a third embodiment, it is possible to provide a "honeycomb " or
channel structuration of the bottom substrate which, after filling
with a single composition of a cholesteric material according to
the invention, allows the pixels to be physically isolated from
each other. Of course, photomodulation of each pixel family may be
obtained in accordance with a "dissociative " process or an
"additive " process, as indicated previously.
EXAMPLE 12
Fourth Embodiment of a Trichromatic Cell
[0107] In the embodiments of examples 9 to 11, the use of pixels
allows a colour display to be obtained, i.e. the perception by the
observer of an image coloured by combining the pixels of a same
image point. The fourth embodiment in a way constitutes a
simplification in that the display surface is divided into several
photomodulable zones each having a sub-family of pixels allowing
information to be displayed in a single determined colour, and thus
to distinguish very simply different categories of information.
This embodiment in no way excludes providing a zone made in
accordance with one of the other three embodiments.
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